Issue Date: July 20, 2015
Challenging Lithium-Ion Batteries With New Chemistry
THere was an odd scene in an engineering building in Oxfordshire, England, recently when a dozen journalists ignored five bronze C-X75 Jaguar supercars set to appear in “Spectre,” the next James Bond film. Instead, the reporters were huddled around a prototype electric-powered bicycle.
While the C-X75s are among the 1.2 billion combustion engine cars on the planet, the electric bike, developed by Oxfordshire start-up Faradion, is the first vehicle ever to be powered by a battery using sodium-ion chemistry.
A few days later and in the same region of England—which boasts numerous technology start-ups attracted by the University of Oxford—Oxis Energy was showing off a developmental technology of its own: a lithium-sulfur battery that powers an airport-style people carrier.
Given the broken promises and collapsed business models that have dogged other battery start-ups in recent years, perhaps such advances are good enough. Moreover, Faradion and Oxis have identified chemical and other modifications to further improve battery performance and reduce costs in the coming years.
With the planned improvements, the two English companies say they will be in a position to solve a critical problem for mainstay lithium-ion batteries: cost, particularly for use in electric cars for the mass market. Industry watchers, however, remain unconvinced that the novel batteries will offer the needed power, recharge ability, and safety. They say the firms will have to prove their technologies in niche applications first.
Should Faradion and Oxis hit their expected performance targets, they could tap into an electric car battery market that by 2023 will be worth $24 billion, according to Navigant Research, a market research firm based in Boulder, Colo.
Lithium-ion battery cathode compositions, such as lithium-nickel-cobalt-manganese, are the materials of choice for Tesla, General Motors, and Nissan, the leading producers of the current crop of electric cars.
Battery developers consider the cathode to be the key to battery performance. As ions move from the anode through the electrolyte and across a separator to the cathode, they generate an electric current. The more ions the cathode can hold, the more energy the battery can store and release.
Faradion says the sodium compounds that make up its cathode are close to matching the energy performance of lithium-ion battery materials but at less than one-tenth the cost. Because most other battery components cost the same, a complete sodium-ion battery would be 30% cheaper, Faradion says.
“Sodium salts are abundant. You are never going to run out,” says Jerry Barker, Faradion’s chief technology officer. Another advantage sodium-ion batteries have is they can be drained to zero charge without damaging the active materials. This means that they can be stored and shipped safely, even by airplane, Barker says.
In contrast, for a lithium-ion battery to remain viable, it must retain about 30% of its charge during storage. It’s enough charge that lithium-ion batteries could short-circuit and catch fire during shipment.
Faradion has made a sodium-ion battery with an energy density—a measure of how much power can be packed into a battery cell—of 140 to 150 watt-hours per kilogram.This compares with about 170 Wh per kg for lithium-ion cells based on cathodes made of lithium cobalt oxide. But the firm is “on track” to hike the density to more than 200 Wh per kg by 2017. “Then it would be comparable with the best lithium-ion,” Barker says.
Faradion, which is funded by the Danish catalysis firm Haldor-Topsøe and the Japanese electronics giant Sharp, acknowledges that it still has much work to do to get there. The firm’s researchers seek to optimize the batteries’ active materials through enhanced particle size distribution. Faradion is also looking at improving porosity and other electrode properties.
Sodium-ion batteries are already where they need to be in their charge-discharge performance. After 1,000 cycles, the battery still delivers 93% of its original energy capacity. “People had a preconception that it would not cycle well over time, but we have shown that it’s equal to lithium-ion,” Barker says. Faradion has been working with chemists at Oxford to maximize battery lifetime.
Oxis, meanwhile, is making “great strides” to increase the energy density of its battery cells to 500 Wh per kg within four years, says David A. Ainsworth, the firm’s chief technical officer. “This is double what any lithium-ion battery can deliver,” he boasts.
Oxis, which has received $24 million in funding from the South African fuel and chemicals firm Sasol, has targeted using half of the material required for the same performance in a lithium-ion battery. Energy density enhancements will come from improvements to the lithium-sulfur cathode plus new additives and solvents in the electrolyte, Ainsworth adds.
Oxis Chief Executive Officer Huw W. Hampson-Jones predicts that the company will be able to cut its battery cell costs to about $125 per kWh in the next few years once its material is manufactured in commercial volumes. Faradion hopes to reduce its sodium-ion cell costs to about $300–$400 per kWh. Lithium-ion batteries currently cost $350–$600 per kWh, industry experts say.
Assuming a car needs a battery with capacity of around 80 kWh, Oxis could offer a cost for a lithium-sulfur battery of about $10,000, considerably less than what the likes of Tesla must pay for its batteries. Hampson Jones expects this figure will be “very attractive” to car manufacturers.
One of the challenges for developers of lithium-sulfur batteries, which feature a lithium-metal anode and a sulfur-carbon cathode, is that they can be unstable and undergo runaway self-heating reactions. Oxis says it has solved this issue and even made its battery material safer than lithium-ion by coating the lithium with a ceramic lithium-sulfide passivation layer and by using a non-flammable electrolyte.
“We’ve never had any thermal runaway issues, even in tests where the cell is penetrated,” Ainsworth says.
He sees Oxis’s main challenge as cycle life. Owners of electric cars expect the battery to store and deliver energy for at least 1,000 charge and discharge cycles with little diminishment in capacity. Oxis’s lithium-sulfur cells currently provide up to 80% of capacity after 1,200 cycles and 60% of capacity after 1,500 cycles.
Even though Oxis is grappling with the cycle life of its lithium-sulfur batteries, military organizations are already interested in using them because they are light and high-powered, Ainsworth says.
Although Oxis and Faradion still have to make up ground on lithium-ion in certain areas of battery cell performance, an advantage that both firms bring is a string of patents and pending patents combined with relatively few competitors in their respective fields. As a result, they can assert strong intellectual property positions and, they hope, avoid litigation.
“This is not the case with lithium-ion, where there could be an intellectual property quagmire,” says Christopher S. Johnson, who heads up a team of sodium-ion battery researchers at Argonne National Laboratory in Lemont, Ill. Indeed, Argonne and BASF are currently suing BASF rival Umicore for alleged patent infringement in the lithium-ion field.
Another potential advantage of lithium-sulfur and sodium-ion technologies is that they have plenty of development runway ahead. “But there is nothing new coming out of lithium-ion—it’s really optimization of what is out there now,” Johnson says.
He also predicts that the performance of sodium-ion batteries in particular could benefit from a surge of research activity now taking place to optimize electrolytes. A blend of propylene carbonate and ether is an example of an electrolytic material that could enhance the performance of sodium-ion batteries. “It’s the tip of the iceberg for electrolytes,” he says. “I think sodium-ion is going to break into niche applications, and eventually the costs will start to win out.”
Johnson’s optimism for sodium-ion is not shared by Lilia Xie, an analyst for Lux Research, a technology market research firm. “Sodium-ion inherently has the disadvantage of lower cell voltages compared to lithium-ion, making it harder to achieve comparable energy densities. I think Faradion’s potential cost reduction claim is tenuous in the near term,” Xie says.
When it comes to Oxis’s lithium-sulfur batteries, Xie considers that Oxis will have its best immediate opportunities in drones and military applications, where weight must be minimized and cycle life is not much of a concern.
The vehicle demonstrations conducted in Oxfordshire, in which the batteries of both Faradion and Oxis performed well within their limits, answered many questions about the new technologies. But the two start-ups know that if they are to prove their doubters wrong, soon they will have to provide automakers with a battery that is reliable, low-cost, and able to safely deliver more power. ◾
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